Blown fuse indicator



June 1962 M. M. WALLER ETAL 3,041,427

BLOWN FUSE INDICATOR Filed April 14, 1965 FIG.I

INVENTORS MILTON M. WALLER NATHAN SC LAR BY KW %w K m ATTORNEYS United States Patent Filed Apr. 14, 1960, Ser. N 0. 22,273 7 Claims. (Cl. 200-121) This invention relates to an indicator for blown fuses and to a combined fuse and indicator.

When one of several fuses has blown, it is often difiicult to identify the blown fuse. Accordingly, a principal object of the present invention is to improve indicators for designating blown fuses.

In accordance with the present invention, a blown fuse indicator is provided which includes a resistive filament of low power capacity in a transparent envelope in shunt with the fuse. An indicating material is intimately secured to the filament. When the fuse blows out, the filament is flashed, and the indicating material applies a distinctive coloring to the transparent envelope. The distinctive coloring may be the result of one or more chemical reactions, and may also involve sputtering as a result of the elevated temperatures present at the filament.

In one specific embodiment of the invention, the filament was of fine tungsten Wire and was coated with a mixture of potassium chlorate and manganese dioxide in equal proportions, by making a water slurry and dipping the filament. When the materials dry, the filament is dipped into a high temperature paint which binds the mixture to the filament and provides a material for oxidation. With this arrangement, when the fuse blows out, the reaction of the potassium chlorate and manganese dioxide provides oxygen and heat, the oxygen reacts with the high temperature paint and provides black carbon particles. The high filament temperature and the vigorous nature of the reaction serves to deposit a permanent indication of black color on the inner wall of the envelope. Advantages of the described blown indicator include substantial independence of the voltage of the circuit; thus, it can readily be used with circuits having a voltage as low as 10 volts. Other advantages include the fact that no current is drawn after the initial current surge, and the additional fact that it is very inexpensive. Furthermore, high sensitivity is attained by the energization of the resistive filament only after the fuse has been blown. 7

Other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description and from the accompanying drawing, in which:

FIG. 1 shows a blown fuse indicator in which the fuse and the indicating filament are in separate envelopes; and

FIG. 2 represents an embodiment of the invention in which the fuse and indicating filament are in the same envelope.

With reference to FIG. 1, the blown fuse indicator system includes a source of voltage 12 which may be either alternating or direct curent, a conventional fuse 14, a separate blown fuse indicator 16 and a load circuit 18. The load circuit 18 is shown as a resistor; however, it would normally be both resistive and inductive. With regard to the blown fuse indicator 16, it includes a base 20, a transparent envelope 22, and a filament 24. The filament 24 is coated with chemically reactive material such as potassium chlorate and manganese dioxide. It is well known that these elements give off oxygen when heated. As mentioned in the introduction to this application, these elements may be applied as a slurry. After they have dried on the filament, the filament may be dipped in a high temperature paint which binds the filament and provides a material for oxidation. For a black 3,041,427 Patented June 26, 1962 indication, the paint may be a paint known as Heat-Rem H170, a paint which is light brown in color prior to flashing. This paint is manufactured by the Specko Ink Co. of Cleveland, Ohio. Many other conventional paints which include organic compounds which are oxidizable to provide black carbonaceous material may also be employed. The fuse 14 has a current rating above 5 amperes. As the filament is much more resistive than the fuse, little current passes through it, and it is not heated to any substantial extent prior to burn-out of the fuse. When the fuse is burned out, this current is applied to the filament 24. The filament is then rapidly brought to white heat and triggers the chemical reaction between the potassium chlorate and manganese dioxide, liberating oxygen. The oxygen reacts with the paint, providing black carbonaceous material which is deposited on the inner surface of the transparent envelope. The tungsten wire forming the filament must have a current rating which is less than the fuse current rating. In the application described, it had a diameter of 0.007 inch, or 7 mils.

It is to be understood that a series of fuses for different circuits and the associated fuse indicator-s may be mounted in a fuse box or the like. The indication provided by the blackened envelope will, under these circumstances, immediately identify the overloaded circuit and the fuse which has been blown out.

The system of FIG. 2 indicates a preferred embodiment of the invention in which the fuse and the blown fuse indicator are included in a single assembly. In the system of FIG. 2, a battery 32 and a load 34 are provided. The blown fuse indicator and fuse assembly includes the transparent envelope 36, the metal base member 38, two heavy conductors 40 and 42 and a lower contact element 44. An insulating washer 46 and insulating potting material 48 are also provided within the metal casing 38. The fusible element 50 and the tungsten filament 52 are connected in parallel between the two heavy conductors 40 and 42. The filament coil is covered with material 54 as described above in connection with the filament 24 of FIG. 1. For this preferred embodiment of FIG. 2, the fuse indicator holder is particularly simple as it need only be a standard bayonet-type lamp socket into which the fuse indicator-fuse assembly is inserted.

In operation, the system of FIG. 2 works in much the same manner as that of FIG. 1. A high degree of sensitivity is obtained by spacing the fusible link and the filament. Thus, even through the fusible element may heat up to some extent, the temperature of the material 54 secured to filament 52 will not be heated to the reactive temperature. This only occurs when fuse 50 is burned out, and filament 52 is flashed by the resulting sudden surge of current through it. The filament 52 is, of course, also burned out so that there is no current drain following burn-out of the fuse.

The filaments 24 and 52 of FIGS. 1 and 2, respectively, may be coated with other materials than those described above. Thus, for example, the coating may be changed in color by the selection of a suitable oxide. In accordance with another embodiment of the invention, colored material may be sputtered directly onto the inner sur face of the transparent envelope without a chemical reaction. In accordance with another embodiment of the invention, a chemical previously present in the envelope, either associated with the filament or on the inner surface of the bulb, may change in color by the liberation of a gas or a solid when the filament is heated. The embodiment described in detail above is a combination of these individual arrangements, as it involves both the change in color of the paint upon liberation of the oxygen, and also involves the sputtering of the resultant material onto the inner surface of the envelope when the filament is flashed.

It is to be understood that the above-described arrange 3 ments are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A combined fuse and indicator comprising a transparent envelope, a pair of spaced heavy conductors extending into said envelope, a fusible metallic element having a given current rating interconnecting said conductors within the envelope, and a resistive filament having a a current capacity below the current rating of said fusible element connected in parallel with said fusible element within said envelope, whereby said filament normally carries less current than said fusible element, said filament being coated with heat reactive means for providing a colorful indication on the inside of said envelope upon burn-out of said fusible element and flashing of said filament in response to a surge of current through the filament following burn-out of said fusible element.

2. A fuse and indicator circuit comprising a pair of conductors, a fusible metallic element having a given current rating interconnecting said conductors, a transparent envelope, and a resistive filament having a current capacity below said current rating of said fusible element connected in parallel with said fusible element and mounted within said envelope whereby said filament normally carries less current than said fusible element, said filament being coated with a heat reactive means for providing a colorful indication on the inside of said envelope upon burn-out of said fusible element and flashing of said filament in response to a surge of current through the filament following burn-out of said fusible element.

3. A fuse and indicator circuit comprising a pair of conductors, a fusible metallic element having a given current rating interconnecting said conductors, a transparent envelope, a resistive filament having a current capacity below said current rating of said fusible element connected in parallel with said fusible element and mounted within said envelope whereby said filament normally carries less current than said fusible element, material of a predetermined color in said envelope, and heat reactive means coated on said filament for changing the color of said material upon flashing of said resistive filament in response to a surge of current following burn-out of said fusible element.

4. A fuse and indicator circuit comprising a pair of conductors, a fusible metallic element having a given current rating interconnecting said conductors, a transparent envelope, a resistive filament having a current capacity below said current rating of said fusible element connected in parallel with said fusible element and mounted within said envelope whereby said filament normally carries less current than said fusible element, and means including a coating on said filament for providing a distinctive coating on the inner surface of said envelope upon flashing of said filament in response to a surge of current through said filament following burn-out of said fusible element.

5. A combined fuse and indicator comprising a transparent envelope, a pair of spaced heavy conductors extending into said envelope, a fusible metallic element having a given current rating interconnecting said conductors within the envelope, a resistive filament having a current capacity below said current rating of said fusible element connected in parallel with said fusible element within said envelope whereby said filament normally carries less current than said fusible element, and means supported by said filament for providing a colorful indication on the inside of said envelope upon burn-out of said fusible element and flashing of said filament in response to a surge of current following burn-out of said fusible element.

6. A combined fuse and indicator comprising a transparent envelope, a pair of spaced heavy conductors extending into said envelope, a fusible metallic element having a given current rating interconnecting said conductors within the envelope, a resistive filament having a current capacity below the current rating of said fusible element connected in parallel with said fusible element within said envelope, and a mixture of manganese dioxide and potassium chlorate and an oxidizable binder material coated on said filament.

7. A combined fuse and indicator comprising a transparent envelope, a pair of spaced heavy conductors extending into said envelope, a fusible metallic element having a given current rating interconnecting said conductors within the envelope, a resistive filament having a current capacity below the current rating of said fusible element connected in parallel with said fusible element within said envelope, a first coating of a mixture of manganese dioxide and potassium chlorate on said filament, and a second coating of paint forming a binder layer on said first coating.

References Cited in the file of this patent UNITED STATES PATENTS 1,033,754 Buchanan July 23, 1912 1,014,741 Barringer et al. Jan. 16, 1912 1,937,178 Vindal Nov. 28, 1933 2,702,329 Dietz et al Feb. 15, 1955 

